[600MRG] Estimating Rr for non-confirming verticals

[Edward R Cole]

Ben,

I have an inverted-L with 43 foot vertical and 122-foot 
horizontal.  I just used EZNEC6-demo to model it.

I got an Rr = 0.8hms and measured R = 20 ohms at resonance.  So 
efficiency = Rr/R = 0.04

I would model you antenna as a T with height of 93.8 foot and top 
wires (whatever they are) long.

The EZNEC program will give Rr.  You have to measure R.  I modified 
my MFL-269B antenna analyze to operate 450-800 KHz and tuned the 
loading coil until I saw minimum reactance (aka resonance):  Z = 20 +/-j0.

EZNEC 6.0-demo is free download.

73, Ed - KL7UW

At 01:12 PM 7/17/2020, Ben Gelb wrote:
>Hi all -
>
>I decided to try feeding my HF dipole (ladder-line fed) as a vertical
>on 630m. I did so, and it works. But I'm wondering a bit about how
>best to estimate Rr, given that the ladder line feed is not actually
>vertical. The first 20 ft or so are close to vertical, followed by a
>roughly 40ft slanted section (45 degrees-ish, though not a straight
>line since it is not held taught - so it follows a catenary curve).
>
>Top load is 93.8'.
>
>That is what I mean by "non-conforming".
>
>So the question is how to reason about this antenna in service of Rr 
>estimation.
>
>Since the whole antenna is pretty small relative to a wavelength,
>perhaps I can get pretty close by decomposing the antenna into its
>vertical and horizontal components? The vertical component (at least
>ignoring that the 45 degress section actually has a nonlinear shape)
>would basically be the height of the dipole feedpoint.
>
>The horizontal component of the ladderline section I imagine would add
>to the effective capacitance of the top loading from the dipole
>(though its more like "mid load" since its not at the top). Perhaps I
>can estimate the increase in effective *top* loading length by
>measuring apparent C of the antenna at the feedpoint - and backsolve
>the equivalent *conforming* T-top antenna (w/ save vertical component)
>that would yield that capacitance. Then use the Rr result for that
>antenna.
>
>Other thoughts?
>
>I could also learn how to use antenna modeling software. But sort of
>fun to try to think about how you might get there intuitively.
>
>73,
>Ben N1VF
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73, Ed - KL7UW
   http://www.kl7uw.com
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